1. Field of the Invention
This invention relates to a control system of a gas turbine engine driven auxiliary electric power unit.
2. Description of the Prior Art
A conventional control system of this kind is disclosed in, for example, U.S. Pat. No. 4,492,874 or U.S. Pat. No. 5,103,629. The gas turbine engine driven auxiliary electric power unit includes a compressor, a turbine and an AC generator which is connected to the turbine through a shaft. The generator is connected to an external power system through an output line. Operation of the gas turbine engine auxiliary electric source unit is directed by a controller. The controller is connected to various sensors of the gas turbine. These sensors monitor various important operating parameters such as temperature, pressure, shaft (rotational) speed and so on. The controller output signals to operational elements of the gas turbine, such as a fuel control and an igniter. As disclosed in U.S. Pat. No. 4,087,961, the fuel control includes a fast acting control valve which controls fuel flow supplied to a combustion chamber for the turbine.
In this gas turbine system, the shaft speed is controlled by means of modulation of the fuel flow by the fast acting control valve of the fuel control. Therefore, in the case when the load is changed and especially when the load is suddenly decreased, the deceleration of the shaft (the gas turbine) by the fuel control does not follow immediately due to slow mechanical response of the gas turbine and fuel control. As a result, the shaft speed increases suddenly and there is a danger the shaft speed temporarily rises to a dangerous or undesirable level. This overspeed phenomenon is a primary concern for the performance of the gas turbine control system.